Forging process for an aluminum alloy part

ABSTRACT

An forging process for an aluminum alloy part. The forging process includes the following steps: S 1 , heating an aluminum alloy blank to a solid solution temperature in a heating device, where, a heating and heat preservation time is determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank is increased by 1 mm; S 2 , conducting underaging heat treatment; S 3 , conducting heating and heat preservation on the aluminum alloy blank obtained after the underaging heat treatment with a forging die at 100-300° C., and preheating a final forging die; S 4 , conducting forming by isothermal forging on the aluminum alloy blank obtained after the heating and heat preservation in step S 3  at 100-300° C.; and S 5 , conducting cooling, trimming and machining on a forged part obtained in step S 4  to obtain the aluminum alloy part.

TECHNICAL FIELD

The present disclosure belongs to the field of hot working of materials,and specifically relates to a forging process for an aluminum alloypart.

BACKGROUND ART

As a non-ferrous metal material most widely used in the industry, analuminum alloy is widely used in aerospace, ships vehicles and othermachinery manufacturing industries. In the automobile manufacturingindustry, the aluminum alloy is usually used to reduce the weight of anautomobile structure, and an aluminum alloy forged part that can bestrengthened by heat treatment is also widely used in automobilemanufacturing. At present, the die forging forming process of aluminumalloys usually involves lots of technological steps. A common dieforging forming process of the aluminum alloy generally includes thefollowing steps: heat treatment before forging, forging forming, solidsolution treatment and aging treatment. In a production process of aheat-treatable aluminum alloy, by conducting homogenization heattreatment, segregation can be eliminated. By conducting heating beforeforging, deformation resistance can be reduced, and the plasticity canbe improved. By conducting heat treatment after the forging, thestrength of a forged part is improved to meet requirements forproperties of a product. In an actual production process, when thisproduction method is used, the time cost and the energy consumption costare high in the heat treatment processes. Therefore, with several timesof the heat treatment in a forging process of the aluminum alloy, thetime consumption is high, the actual production period is prolonged, andthe production cost is increased.

SUMMARY

In view of the problems of long production period and high energyconsumption caused by heating several times in a current aluminum alloyforging pressing process, an objective of the present disclosure is toprovide a forging process for an aluminum alloy part. By using theprocess, the production period can be shortened, and the productionefficiency can be improved.

In order to achieve the objective above, the present disclosure adoptsthe following technical solution. A forging process for an aluminumalloy part includes the following steps:

-   -   S1, heating an aluminum alloy blank to a solid solution        temperature in a heating device, where, a heating and heat        preservation time is determined according to a wall thickness of        the aluminum alloy blank and prolonged by 20 min when the wall        thickness of the aluminum alloy blank is increased by 1 mm;    -   S2, conducting underaging heat treatment;    -   S3, conducting heating and heat preservation on the aluminum        alloy blank (called a part when the step of pre-forging forming        is added) obtained after the underaging heat treatment with a        forging die at 100-300° C., and preheating a final forging die;    -   S4, conducting forming by isothermal forging on the aluminum        alloy blank (part) obtained after the heating and heat        preservation in step S3 at 100-300° C.; and    -   S5, conducting cooling, trimming and machining on a forged part        obtained in step S4 to obtain the aluminum alloy part (a final        product).

According to the technical solution above, the forging process for analuminum alloy part further includes conducting pre-forging formingafter step S1, where, a die is heated to a forging temperature of200-500° C., and the aluminum alloy blank is cooled to a pre-forgingtemperature of 200-450° C. and subjected to the pre-forging forming.Then, the underaging heat treatment is conducted on a pre-forged part.

The aluminum alloy is a 6,000 series aluminum alloy, including anunderaged T4 state and a peak-aged T6 state.

In step S1, the heating and heat preservation time is controlled within90 min.

In step S2, the underaging heat treatment is conducted at a temperatureof 100-300° C., and a heat preservation time is controlled within 2-8 h.A specific temperature is determined according to a position of anexothermic peak precipitated in a corresponding GP zone to ensure thatafter the underaging heat treatment, a precipitated phase only has theGP zone and few β″ phases.

In step S3, a heat preservation temperature and a final forgingtemperature are determined according to a position of an exothermic peakprecipitated in a corresponding β″ zone, the temperature is controlledto ensure that a β′ phase is not further precipitated, and the heatpreservation is conducted within 1-10 min.

In step S3, the final forging die is preheated at a temperature of 200°C.

The precipitated phase of the aluminum alloy is a main factor affectingthe strength, and the size, type and quantity of the precipitated phaseare direct reasons affecting the strength. However, the type, size,quantity and other factors are closely related to a heat treatmentprocess and a forming method of the aluminum alloy. Therefore, the typeand quantity of the precipitated phase of the aluminum alloy can beadjusted through deformation at different heat treatment and processingforming stages. At a heat treatment stage before the forming, theprecipitated phase with a certain size reaches an underpeak aging stagethrough appropriate heat treatment. At a subsequent forming stage, theprecipitated phase of the aluminum alloy not only has great formabilityin preheating and forming processes at an appropriate temperature, butalso can be prepared into a desired product. In addition, the internalprecipitated phase of the aluminum alloy is further evolved to achieve apeak aging effect.

A precipitated strengthening phase of the 6,000 series aluminum alloy isMg₂Si, which is sequentially changed from the GP zone into the β″ phase,the β′ phase and a β phase. When the temperature is increased, the sizeof the strengthening phase is gradually increased, the well-coherent β″phase is substituted with the semi-coherent β′ phase and the incoherentβ phase, and as a result, the strength is greatly reduced. Therefore, alarge number of the β″ phases that are well coherent with a matrix canbe obtained by controlling the type and quantity of the precipitatedphase to ensure a precipitation strengthening effect, and a part meetingrequirements for strength is obtained.

By using the process of the present disclosure, a deformation processand a heat treatment control process of an aluminum alloy forged partare synergized. The type and quantity of the precipitated phase of thealuminum alloy are adjusted through deformation at different heattreatment and processing forming stages to ensure the precipitationstrengthening effect and realize rapid hot forming. The productionperiod can be shortened, the production cost can be reduced, and theproduction efficiency is improved.

According to the present disclosure, rapid hot forming of the aluminumalloy is realized. Compared with an existing widely used forgingprocess, the present disclosure has the following beneficial effects.Generally, heating before forging, solid solution treatment andartificial aging treatment need to be conducted on a blank beforeforging forming, and it takes at least ten hours to strengthen the blankby heat treatment. However, when the rapid hot forming is conducted byusing the process of the present disclosure, not only is a heattreatment process reduced, but also the artificial aging time isshortened. In general, under the condition of ensuring properties of amaterial, not only can the period of the entire forging processshortened, but also the energy consumption required for the heattreatment can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a general forging forming process of anexisting aluminum alloy.

FIG. 2 is a diagram showing a processing flow of a simple part inExample 1 of the present disclosure (the left half part is a flowdiagram, and the right half part is a diagram showing a temperature-timecurve).

FIG. 3 is a diagram showing a processing flow of a complex part inExample 2 of the present disclosure.

FIG. 4 a is a physical diagram showing a trial-produced control arm inExample 3 of the present disclosure.

FIG. 4 b is a diagram showing a sampling area of a tensile sample inExample 3 of the present disclosure.

FIG. 4 c is a diagram showing a size of the tensile sample in Example 3of the present disclosure.

In the figures, P—blank; Stp.1—Conduct heating and heat preservation;Stp.2—Pre-forge; Stp.3—Final forge; Stp.4—Solid solution treatment;Stp.5—Aging treatment; Stp.11—Heat to a solid solution temperature andconduct heat preservation; Stp.21—Forge.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure is further described below with reference toaccompanying drawings and examples.

Example 1

For a simple part requiring only die forging once, a forging process foran aluminum alloy part included the following steps (as shown in FIG. 2):

-   -   S1, an aluminum alloy blank was heated to a solid solution        temperature (for solid solution treatment) in a heating device,        where, a heating and heat preservation time was determined        according to a wall thickness of the aluminum alloy blank and        prolonged by 20 min when the wall thickness of the aluminum        alloy blank was increased by 1 mm, the aluminum alloy was a        6,000 series aluminum alloy, and the heating and heat        preservation time was controlled within 90 min;    -   S2, underaging heat treatment was conducted on the aluminum        alloy blank at a temperature of 100-150° C. for 2-8 h;    -   S3, heat preservation was conducted on the aluminum alloy blank        obtained after the underaging heat treatment at 200-250° C. for        5-10 min, and a forging die was preheated to 200° C.;    -   S4, final forging forming was conducted by isothermal forging on        the aluminum alloy blank obtained after the underaging heat        treatment at 100-300° C.; and    -   S5, cooling, trimming and machining were conducted on a forged        part to obtain a final product of an aluminum alloy part.

A processing flow in this example was shown in FIG. 2 .

A precipitated strengthening phase of the 6,000 series aluminum alloywas Mg₂Si, which was sequentially changed from a GP zone into a β″phase, a β′ phase and a β phase. When the temperature was increased, thesize of the strengthening phase was gradually increased, thewell-coherent β″ phase was substituted with the semi-coherent β′ phaseand the incoherent R phase, and as a result, the strength was greatlyreduced. A supersaturated solid solution was formed by the solidsolution treatment. By controlling the temperature and time of theunderaging heat treatment, the GP zone was converted into about 70%-80%of the β″ phase. Finally, by controlling the temperature and time offinal forging, the remaining GP zone was further converted into about95% of the β″ phase. The generation of the β′ phase and the β phase witha low precipitation strengthening effect was avoided, the purpose ofensuring the precipitation strengthening effect was achieved, and thus,properties of a material were ensured.

Example 2

For a complex part requiring die forging several times, an forgingprocess for an aluminum alloy part included the following steps (asshown in FIG. 3 ):

-   -   S1, solid solution treatment was conducted on an aluminum alloy        blank in a heating device, where, a heating and heat        preservation time was determined according to a wall thickness        of the aluminum alloy blank and prolonged by 20 min when the        wall thickness of the aluminum alloy blank was increased by 1        mm, and the aluminum alloy was a 6,000 series aluminum alloy;    -   S2, a die was heated to a forging temperature, and the aluminum        alloy blank obtained after the solid solution treatment was        cooled to a pre-forging temperature of 450° C. and subjected to        pre-forging forming;    -   S3, underaging heat treatment was conducted on a part obtained        after the pre-forging forming at a temperature of 100-150° C.        for 2-8 h;    -   S4, heat preservation was conducted on the part obtained after        the underaging heat treatment at 200-250° C. for 5-10 min, and a        final forging die was preheated to 200° C.;    -   S5, final forging forming was conducted by isothermal forging on        the part obtained after the underaging heat treatment; and    -   S6, cooling, trimming and machining were conducted on a forged        part to obtain the aluminum alloy part (a final product).

Where, the time of transferring the forged part between dies duringseveral times of the die forging needed to be as short as possible toavoid the situation that when the transfer time was too long, thetemperature was reduced too fast, and the mechanical property of thepart was affected.

A processing flow in this example was shown in FIG. 3 .

By analyzing a DSC curve of a sample based on the solid solutiontreatment and the underaging heat treatment, it could be seen that afterthe underaging heat treatment, a precipitated peak in a GP zone in asolid solution state disappeared, indicating that the GP zone was formedin a supersaturated solid solution state and partially converted into aβ″ phase. When the aging time was longer, the conversion amount waslarger. In addition, at an appropriate temperature, when the aging timewas longer, the quantity of the β″ phase was increased. When a largenumber of the GP zones and few β″ phases were generated during the agingtreatment, a sample formed after heat preservation at 200-250° C. for acertain period of time had high hardness. Besides, the hardness of theformed sample was greatly affected by a forming temperature. When thetemperature was high, a precipitated phase was converted into a β′ phasewith a low strengthening effect.

According to lots of experimental results, it could be seen that byusing this method sequentially including the underaging heat treatment,the heat preservation at an appropriate temperature and the forming,great formability could be achieved, the mechanical property of thesample formed by compression was great, and an evolution process of theprecipitated phase could be optimally controlled. Compared with atraditional method of adjusting properties by sequentially conductingforming and heat treatment, the method had higher efficiency and lowerenergy loss.

Example 3

When a 6,082 aluminum alloy was used as an aluminum alloy blankmaterial, an forging process for an aluminum alloy part specificallyincluded the following steps and parameters:

-   -   S1, solid solution treatment was conducted on the aluminum alloy        blank at 535° C. in a heating device, where, a heating and heat        preservation time was determined according to a wall thickness        of the aluminum alloy blank and prolonged by 20 min when the        wall thickness of the aluminum alloy blank was increased by 1        mm;    -   S2, pre-forging forming was conducted on the aluminum alloy        blank obtained after the solid solution treatment at 450° C.;    -   S3, underaging heat treatment was conducted on a part obtained        after the pre-forging forming at a temperature of 120±5° C. for        4-6 h;    -   S4, heat preservation was conducted on the part obtained after        the underaging heat treatment at 200±5° C. for 5-10 min, and a        final forging die was preheated to 200° C.;    -   S5, final forging forming was conducted by isothermal forging on        the part obtained after the underaging heat treatment at        100-300° C.; and    -   S6, cooling, trimming and machining were conducted on a forged        part to obtain the aluminum alloy part (a final product).

A trial-produced sample (as shown in FIG. 4 a , FIG. 4 and FIG. 4 c ) ofan automobile control arm was obtained according to Example 3. Aroom-temperature tensile test and a hardness test were carried out onthe forged part. The room-temperature tensile test was completed in ametal room-temperature tensile machine and carried out three times toobtain an average value. The sample had a tensile strength of 335 MPaand a yield strength of 305 MPa. In addition, a surface of the samplewas polished and smoothed to test the hardness. It was tested that thesample had a hardness of 120 HV. According to the tensile test and thehardness, it was shown that a trial-produced control arm had greatmechanical property, and requirements for properties of a product weremet. Results were shown in the following Table 1.

TABLE 1 Mechanical property requirements and measurement results TensileYield strength strength Test item Rm Rp Hardness Technical requirements≥330 MPa ≥290 MPa ≥100 HV Measurement results   335 MPa   305 MPa   120HV

According to Table 1, it was indicated that by using the process of thepresent disclosure, properties of a material could be ensured.

It should be understood that those of ordinary skill in the art can makeimprovements or transformations based on the above description, and allthese improvements and transformations should fall within the protectionscope of the appended claims of the present disclosure.

What is claimed is:
 1. A forging process for an aluminum alloy part,comprising the following steps: S1, heating an aluminum alloy blank to asolid solution temperature in a heating device, wherein, a heating andheat preservation time is determined according to a wall thickness ofthe aluminum alloy blank and prolonged by 20 min when the wall thicknessof the aluminum alloy blank is increased by 1 mm; S2, conductingpre-forging forming after step S1, wherein, a pre-forging die is heatedto a forging temperature, and the aluminum alloy blank is cooled to apre-forging temperature of 200-450° C. and subjected to the pre-forgingforming; S3, conducting underaging heat treatment at a temperature of100-300° C., wherein, a heat preservation time is controlled within 2-8h, and a specific temperature is determined according to a position ofan exothermic peak precipitated in a corresponding GP zone to ensurethat after the underaging heat treatment, a precipitated phase only hasthe GP zone and few β″ phases; S4, conducting heating and heatpreservation on the aluminum alloy blank obtained after the underagingheat treatment at 100-300° C., and preheating a final forging die;wherein, a heat preservation temperature and a final forging temperatureare determined according to a position of an exothermic peakprecipitated in a corresponding β″ zone, the temperature is controlledto ensure that a β′ phase is not further precipitated, and the heatpreservation is conducted within 1-10 min; S5, conducting final forgingforming by isothermal forging on the aluminum alloy blank obtained afterthe heating and heat preservation in step S4 at 100-300° C.; and S6,conducting cooling, trimming and machining on a forged part obtained instep S5 to obtain the aluminum alloy part.
 2. The forging process ofclaim 1, wherein, the aluminum alloy is a 6,000 series aluminum alloy.3. The forging process of claim 1, wherein, in step S4, the finalforging die is preheated at a temperature of 200° C.